Electrical circuit interconnect system

ABSTRACT

An assembly for mounting components to a microwave circuit, using plated through bore holes that extend from the ground plane of the circuit through the insulating substrate to the surface on which the components are mounted. The components have a conductive outer surface that functions as its ground plane. This surface is in electrical contact with the plated through bore holes, creating a uniform ground plane between the microstrip circuit and the component. The insulating dielectric can be provided with a recess in which the component can be housed. The base of the recess can be plated and the plated through bores connected between the cavity plating and the ground plane. The component can then be positioned inside the recess so its ground plane is in contact with plating so as to form a uniform ground plane between the circuit and the component.

FIELD OF THE INVENTION

This invention relates to an assembly for mounting components to anelectrical circuit, and in particular it relates to an assembly forconnecting components to a microwave circuit formed from microstriptransmission lines.

BACKGROUND OF THE INVENTION

Microstrip transmission lines are frequently used as bases for microwavecircuits. These lines comprise one or more flat conductors that areseparated from a ground plane by an insulating dielectric or substrate.An important advantage of microstrip transmission lines is theirrelatively low cost since the circuits can be made by etched circuittechniques. Another important advantage is their structural rigidity,which provides circuit stability in the face of external forces.Furthermore, by varying the lengths, widths, and shapes of theconductors, and by proper positioning of adjacent conductors, discretecomponents such as capacitors, inductors and couplers can be formed outof microstrip transmission line segments.

Currently, however, there are limitations to the use of microstriptransmission lines. Discrete components, such as diodes, are difficultto shunt to microstrip circuits. It has been necessary to mount thecomponent on a pedestal and place the resulting subassembly in abored-out section of dielectric in which the ground plane is exposedfrom above. The subassembly is then secured in the bore so that thediode is in electrical contact with the conductor and the pedestal is inelectrical contact with the underlying ground plane.

Furthermore, a sizeable amount of electromagnetic radiation may bepropagated or received by a component mounted according to this system.This is significant because inductive coupling between adjacentmicrowave components, caused by the emission and reception ofelectromagnetic radiation, may adversely affect the operatingcharacteristics of the individual components. The only way to eliminatethe inductive coupling is to electrically isolate the individualcomponents. Often the only way to do this is to distance the componentsaway from each other. This makes it difficult to provide a miniaturizedcircuit on the microstrip.

Also, it is often desirable to integrate different dielectric materialsinto a single circuit. For example, with a microstrip circuit having aceramic dielectric, it may be desirable in short sections of the circuitto take advantage of the different characteristics of material such asfused quartz, plastic, beryllium oxide, or other dielectrics.Previously, it has proved difficult to provide a microwave circuit withmore than one type of insulating dielectric. When it has been necessaryto provide a circuit with more than one dielectric, a separate circuitwould have to be provided for each dielectric.

Furthermore, it is sometimes necessary to provide a microwave circuitwith more than one type of transmission line. For example, it may bedesirable to provide a circuit composed primarily of microstrip, withshort lengths of coaxial line or stripline, which are other forms ofmicrowave transmission lines. Currently, there is no convenient way toprovide an integrated circuit having more than one type of transmisionline. When it is necessary to use more than one type of transmissionline, more than the one circuit must be used.

Also, it is often desirable to connect a microwave circuit to othercircuits in order to assemble a complete electronic device. Often theseconnections are made by way of coaxial cables. It is then necessary toprovide coaxial feed-through connectors between the microwave circuitsand the cables to which they are connected. Since these feed-throughsare separate components, they have their own inductive couplingcharacteristics that affect the operation of the circuits. Furthermore,it is costly to electrically connect a feed-through to a circuit, and tomechanically connect it to a circuit's housing.

Additionally, it is sometimes desirable to provide a conventional,non-microwave, circuit, such as one made with a printed wire board, withone or more microwave components. At the present it is difficult tomount such components to such a circuit because the electromagneticradiation they receive and propagate affects the operation of the entirecircuit. As a result it is necessary to mount any microwave componentsthat are part of a conventional circuit to a separate circuit board sothey are electrically isolated from the nearby components.

A need therefore exists for a new electrical circuit interconnectionsystem so that components can be readily connected to a microstripcircuit. The system should allow for the components to be readilyconnected to both the conductor and the ground plane. Theinterconnection system should also provide a sufficient degree ofelectrical isolation so the effects of inductive coupling will beminimal. Alternatively, the system should provide total electricalisolation of components so as to eliminate all inductive couplingbetween adjacent components. This would provide a means for integrallymounting a set of microwave components to a conventional circuit.

Furthermore, the system should allow for sections with differentdielectrics, or sections of different types of transmission lines to beconnected to the basic stripline microwave circuit. The interconnectionsystem should also make it possible to readily connect a coaxialfeed-through connector to a microstrip circuit so that it is an integralpart of the circuit.

SUMMARY OF THE INVENTION

A circuit interconnect system embodying this invention comprises arecess on the circuit dielectric in which the component to be installedis inserted. The base of the recess is plated, and is in electricalcontact with the adjacent ground plane through at least one plated holethat extends through the dielectric. A component can be connected to thecircuit by inserting it into the recess and electrically connecting itto adjacent conductors. The base of the component has a ground planethat is in contact with the plated base of the recess. The plated holesprovide a low-impedance path between the component ground and thecircuit ground so as to form a common ground between them.

The invention thus eliminates the need to provide pedestals for discretecomponents. It also makes it possible to provide a circuit with sectionsformed with different dielectric materials or with differenttransmission types, by treating these sections as components andmounting them in the same way.

Another advantage of the invention is that each component in the systemmay be electrically isolated within the circuit. The common groundbetween the component and the circuit attenuates the electromagneticradiation that is propagated or received by the component. Thus, thedegree of inductive coupling of components mounted according to thissystem is minimal. Alternatively, this system allows for the totalisolation of a component on a microstrip circuit by encapsulation. Thiscan be done by providing a conductive shield around the component on thesurface of the dielectric. The shield is connected to the circuit groundplane by plated holes so both the reception and generation of spuriouselectromagnetic waves by the component is blocked.

It would also be possible to provide a simplified attachment of acoaxial cable connector. The ground plane of the circuit can be extendedaround the edge of the dielectric and over to the outer perimeter of thesurface carrying the conductor. A coaxial feed-through connector can behoused in a semi-circular cut formed within the ground plane. Since theouter shell of the feed-through serves as its ground plane and is indirect contact with the ground plane of the circuit, a connector mountedaccording to this system is an integral part of the circuit.

This system also makes it possible to mount individual microwavecomponents, or a microwave subcircuit, to a conventional circuit. Themicrowave components or sub-circuit can be housed in a miniaturehousing. The housing is formed of conductive material so its contentswould be electrically isolated from the outside environment. The housingcan then be mounted to the conventional circuit without the risk ofspurious electromagnetic radiation affecting the operation of either themicrowave or non-microwave circuit components.

This system can also be readily adapted to provide isolation cavitiesfor other types of electrical transmission lines.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a microstrip circuit containing anelectrical component connected according to this invention.

FIG. 2 is a cross-sectional view of a microstrip circuit containing astripline transmission line mounted according to this invention.

FIG. 3 is a cross-sectional view of a microstrip circuit containing alength of microstrip having a dielectric different than that of basecircuit mounted according to this invention.

FIG. 4 is an exploded top isometric view of a microstrip circuitcontaining a hermetically shielded component mounted according to thisinvention.

FIG. 5 is a longitudinally extending cross-sectional view of amicrostrip circuit containing an inverted microstrip mounted accordingto this invention.

FIG. 6 is a laterally extending cross-sectional circuit with a view of amicrostrip circuit with a section of inverted microstrip mounted to ittaken along line 6--6 of FIG. 5.

FIG. 7 is an exploded top isometric view of microstrip circuit with acoaxial feed-through connector and a cover mounted according to thisinvention.

FIG. 8 is a cross-sectional view of a microstrip circuit containing acoaxial transmission line mounted according to this invention.

FIG. 9 is a longitudinally extending cross-sectional view of amicrostrip circuit containing a shielded section of microstrip mountedwithin the circuit according to this invention.

FIG. 10 is a laterally extending cross-sectional view of the microstripcircuit of FIG. 9 taken along line 10--10.

FIG. 11 is a top view of the microstrip circuit of FIGS. 9 and 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a basic microstrip transmission line 10 comprisingconductors 12 separated from a ground plane 14 by an insulatingsubstrate, or dielectric, 16. The conductors and ground plane are formedof a metal, typically copper, and the insulating dielectric is composedof a ceramic or other suitable material. According to the interconnectsystem of this invention, an electrical component, here a diode 18, ismounted within a recess 20 formed in the dielectric 16. The recess 20has a depth such that the top of the diode 18 is substantially coplanarwith the top surface of the transmission line 10. The diode is connectedto the conductors 12 by a conductive ribbon 22 that extends between abonding point 24 on the diode and adjacent points on the conductors 12.The diode 18 is provided with a planar ground conductor 26 that isconnected to the circuit ground plane 14 through a conductive disc 27 atthe base of the recess.

More specifically, the base of the recess 20 is provided with aconductive plating 28. The disc 27 is attached to the conductiveplating. Plated holes 30, that extend through the dielectric 16, providea low-impedance path between the plating 28 and the circuit ground plane14. The plating 28 is preferably formed by plating at the same time thatthe holes 30 are plated. The plating 28 is in effect an offset portionof the ground plane 14 and by contacting the plating 28, the diodeground conductor 26 is thus connected to the ground plane.

There are a number of advantages to the interconnect system of thisinvention. It eliminates the need to provide a pedestal when mounting acomponent in a microstrip circuit. Also, the component is housed insidea cavity that is shallow by comparison with the standard bore thatcomponents are currently housed in. This reduces the difficulty ofconnecting the component to ground plane.

Furthermore, the recess plating 28 and plated holes 30 provide alow-impedance path between the component ground plane 26 and the circuitground plane 14. In effect, therefore, the component 18 has a commonground with the rest of the circuit. The disc 27 prevents any moisturefrom seeping into the component. If the plated holes are spaced lessthan one-half a wave length apart of the circuit's highest operatingfrequency there is only a minimal possibility of the ground planedeveloping a current that could affect the operation of the circuit.Therefore, the propagation and reception of stray electromagneticradiation by the component is significantly reduced. Also due to thehole side wall plating components can be spaced together more closelythan was previously possible.

As illustrated by FIG. 2, a section of stripline 32 may be mounted on amicrostrip circuit 34 in accordance with this invention. The striplinesection 32 consists of a center conductor 36 embedded between two layersof dielectric 38, with ground planes 40 and 41 on the exposed sides ofthe dielectrics. The top ground plane 40 is connected to the bottomground plane 41 by conductive pins 42 that extend through thedielectrics and are spaced away from the conductor 36. The striplinesection is mounted in a recess 20a formed by the circuit dielectric 16so that one dielectric layer 38 and the bottom ground plane 41 arewithin the recess. The stripline conductor 36 is connected to theadjacent microstrip circuit conductors 12 by the ribbons 22. The bottomground plane 41 is in contact with the recess plating 28 that isconnected to the circuit ground plane 14 through the plated holes 30.

As is illustrated in FIG. 8, it is similarly possible to mount a section104 of coaxial line on a microstrip circuit 106 in accordance with thisinvention. The coaxial line section comprises a center conductor 108coaxial an outer ground conductor or shield 112. A cylindricaldielectric 110 is disposed with the space between the conductors 108 and112. The coaxial section 104 is mounted in a recess 20e in the circuitdielectric 16. The conductive ribbons 22 are used to connect theterminal ends of the coaxial center conductor 108 to the adjacentcircuit conductors 12. The coaxial shield 112 contacts the recessplating 28 that is connected to the circuit ground plane 14 through theplated holes 30. It may be desirable to provide an insulated covering(not illustrated) around the portion of the coaxial shield 112 thatprojects above the surface of the dielectric 16.

As shown in FIG. 3, a microstrip circuit 44 may have a section 46 with adielectric formed of different material than that used in the basemicrostrip. For example, the base microstrip 44 may have a dielectric 16formed from ceramic or plastic, and the section 46 have either a fusedquartz or beryllium oxide dielectric 48. The section 46 is housed insidethe recess 20b in the circuit dielectric 12 and it has a conductor 50connected to the adjacent circuit conductors 12 by the ribbons 22. Thesection 46 has a ground plane 52 that contacts the plating 28 at thebase of the recess 20b. Again, the plated holes 30 provide alow-impedance path from the section ground plane 52 and recess plating28 to the circuit ground plane 14.

As illustrated in FIGS. 9, 10 and 11, it is also possible to mount amicrostrip section 118 with a component 119 wholly within a recess 20fof a microstrip circuit 120. The microstrip section 118 has a dielectric122 that has a vertical profile substantially less than that of a recess20f. The dielectric may also have a width less than that of the recess20f. The microstrip section 118 also has a conductor 124 on the topfirst surface of the dielectric 122 and a ground plane 126 that subtendsthe base of the dielectric 122. The component 119 may be mounted to themicrostrip section 118 in any manner convenient to the circuit design.The section conductor 124 is connected to the circuit conductor 12 bythe ribbons 22. The section ground plane 126 contacts the recess plating28.

The recess 20f is provided with side wall plating 80, integral with thebase plating 28. The side wall plating 80 is disposed around most of thevertical side walls of the recess 20f. Additional shielding is providedby surface plating 84 on the dielectric 16 adjacent the recess 20f thatis an extension of the side wall plating 80. Plated holes 66, thatextend completely through the circuit dielectric 16, provide alow-impedance path between the surface shielding 84 and the ground plane14. A transmission line section mounted according to this embodiment ofthis interconnect system is thus electrically isolated from spuriouselectromagnetic radiation on three sides.

Thus, this interconnect system also makes it possible to mixtransmission lines on a base microstrip circuit, or provide sectionswith a different dielectric than the base circuit. The transmission linesection 32, 46, 104, or 118 is mounted within the appropriate recess 20as if it was a component. The recess plating 28 and the plated holes 30provide a low-impedance path from the section ground plane or shielding41, 52, 112 or 126 to the circuit ground plane 14 so that the section oftransmission line mounted to the circuit has a ground plane that isintegral with the circuit ground plane.

As is illustrated in FIG. 4, it is also possible to electrically isolatea component with a hermetic seal. Here, an individual component, such asthe diode 18 is housed inside the recess 20 of a microstrip circuit 56as previously described. A hermetic seal 54 includes a side wallenclosure 57 formed of an electrically conductive material, such asaluminum, that is suitably sealed to the dielectric 16 around thecomponent 18. Feed-throughs 58 are provided at the base of the enclosure57 so the component 18 can be connected to the external circuitconductors 12. Specifically, a conductive ribbon 60, encased within aninsulating glass bead 62 within each feed-through provides a conductivepath interconnecting the conductors 12 internal to and external to theenclosure 57. A cover 64, also of electrically conducting material, issealed over the top of the enclosure 57. Plated holes 66, that extendbetween the surface of the circuit dielectric 16 underneath theenclosure 57 and the circuit ground plane 14, provide a low-impedancepath between the seal 54 and the circuit ground plane.

As is illustrated in FIGS. 5 and 6, a component may also be electricallyisolated by mounting it on a section of inverted microstrip and mountingthe inverted microstrip to a base circuit. An inverted microstrip 68comprises a conductor 72 fastened to the bottom of an insulatingdielectric 74, with a ground plane 76 on top of the insulatingsubstrate. The ground plane 76 is part of a ground plating 81 thatextends around the edges of the dielectric 74 and on to the perimeter ofthe substrate surface on which the conductor 72 is mounted. A component78 may be mounted to the inverted microstrip in any manner convenient tothe circuit design. A recess 20d accommodating the component is providedwith the recess plating 28 and with side wall plating 80, integral withthe base plating, that extends at least partially around the walls ofthe recess. Surface plating 84 is provided on the dielectric adjacentthe recess 20d.

The inverted microstrip 68 is mounted on the base circuit 70 so that thecomponent 78 is within the recess 20d, the inverted microstrip conductor72 overlaps adjacent circuit conductors, and the inverted microstripplating 81 overlaps the adjacent circuit surface plating 84. Platedholes 30 between the recess plating 28 the circuit ground plane 14 andplated holes 66 between the surface plating 84 and the ground planeprovide a low-impedance path between the platings 28, 80, 81 around thecomponent and the ground plane 14.

An advantage of the aforesaid embodiments of this invention is that acomponent is mounted to the circuit within an electrically groundedcavity. Thus, the component will not be affected by the reception orpropagation of electromagnetic radiation to or from nearby components.

As is illustrated in FIG. 7, a coaxial feed-through connector 86 may bemade an integral part of a microstrip circuit 88. The circuit groundplane 14 is part of a ground plating 92 that extends around the edges ofthe dielectric 16 and over the outer perimeter of the dielectric surfacecarrying the conductors 12, so as to form a lip 94 at least partiallyaround the dielectric. A semi-circular cut 95 is formed in the lipadjacent the conductors to be connected to a coaxial line. Thefeedthrough 86 comprises a conductive cylinder 96 for connection to thecoax shielding and a pin 98 extending axially through the cylinder forconnection to the coax conductor. A glass spacer 100 may be disposedaround the pin 98 to secure it in, and insulate it from, the cylinder96.

The feed-through 86 is attached to the circuit with the cylinder 96secured to the frame within the cut 95 and the transmission pin 98 is incontact with the terminal end of the circuit conductor 12. Plated holes66 adjacent the cut 95 extend between the lip 94 and the circuit groundplane 14 to provide a short, low-impedance path between the feed-through86 and the ground plane.

A cover 102, of electrically conductive material may be provided overthe top of the circuit 88 to provide mechanical protection andelectrical isolation. The cover includes a lip 104 that extends aroundthe outer perimeter of the cover and is sealed to the circuit lip 94. Asemi-circular indenture 106 in the lip is adjacent the circuit groundplane cut 95 so the feed-through 86 may be accommodated. A number ofplated holes 66, extending from the circuit lip 94 and the circuitground plane 14 around the dielectric 16 provide a low-impedance pathbetween the cover 102 and the ground plane.

The plated holes 66 provide a low-impedance conductive path from thefeed-through 96 and the cover 102 to the ground plane so they areelectrically integral with it. The circuit ground plane lip 94 and thecover lip 104 can be extended over the surface of the dielectric asufficient distance to eliminate any propagation or reception of strayelectromagnetic radiation by the enclosed circuit. In such instances theplated holes 66 provide a low-impedance path between the inner edges ofthe circuit lip 94 of the ground plating 92 and the ground plane 14.

This system prevents the lip 94 and the region beneath it fromelectrically affecting the operation of the circuit through thegeneration of unwanted electromagnetic waves. Thus a complete, protectedmicrostrip circuit with external connectors can be isolatedelectrically, thereby avoiding unwanted reception or propagation ofspurious electromagnetic radiation. This makes it possible toconveniently and economically connect microstrip circuits to othercircuits in order to assemble an electronic device. Furthermore, thehousing and feed-through connector assembly of this invention can besufficiently miniaturized so an electronically isolated microwavesubcircuit can be directly connected to a conventional, non-microwavecircuit assembly.

Alternative embodiments of this invention can be provided withoutdeparting from the scope of the claimed invention. For example, theplated through bore holes can be replaced with solid conductors having astar-shaped cross section or any other conductor that can provide alow-impedance path to the ground plane. In some situations it may not benecessary to provide the disc 27 at the base of the recess. Also, therecess side wall plating 80, surface plating 84 and plated holes 66 maybe provided in instances where it is desirable to further shield acomponent housed in the recess 20. Furthermore, other types ofcomponents and transmission lines may be connected to a microstripcircuit according to the interconnect system of this invention thanthose described.

Also, the interconnect system of this invention is not limited to solelymicrostrip or even microwave circuits. This system may be used with anycircuit where two or more conductors are spaced apart from each other bydielectric layers. For instance, in a stripline circuit a plated hollowmay be formed around a center conductor and a component may be mountedwithin the hollow. A set of low-impedance paths leading from the hollowto the circuit ground planes would turn the hollow into an electricalcavity isolated from external electromagnetic radiation.

Alternatively, a conventional printed wire board circuit may have asignal conductor and a ground conductor located on the opposite sides ofa substrate board. A recess may be formed in the surface of thesubstrate carrying the signal conductor. The recess would be plated andthe plating connected to the ground conductor by one or morelow-impedance paths that extend through the substrate. Thus an isolationcavity would be formed on the surface of the substrate carrying thesignal conductor. A component mounted in the recess would thus beisolated from the propagation or reception of spurious electromagneticradiation. Therefore, it is intended that all matter contained in theabove description or shown in the accompanying drawings be interpretedas illustrative and not in a limited sense.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. An interconnection assembly for mounting acomponent to an electrical circuit, the circuit comprising at least oneconductor on a first surface of an insulating substrate and a groundconductor over a second surface of the insulating substrate oppositesaid first surface, the assembly comprising:(a) means forming a recessin the first substrate surface; (b) a component disposed at leastpartially within said recess, the component including an external groundsurface in electrical contact with said recess; (c) conductive platingon said first substrate surface at the base of said recess in contactwith said component external ground surface; and (d) a low-impedanceconductive path between said conductive plating and said circuit groundconductor extending through said insulating substrate.
 2. The assemblyof claim 1 wherein said conductive path is formed from at least oneplated hole that extends between said conductive plating and the groundconductor.
 3. The assembly of claim 1 wherein said component groundsurface is in electrical contact with said recess through a conductivedisc located at the base of said recess.
 4. The assembly of claim 1wherein said electrical circuit is a microstrip circuit and said groundconductor is a conductive ground plane disposed at least partially oversaid substrate second surface.
 5. The assembly of claim 1 wherein saidcomponent comprises an electrical transmission line including aconductor and a conductive ground plane separated by a dielectric. 6.The assembly of claim 5 wherein said transmission line is disposed atleast partially in said recess, said transmission line being adapted tobe electrically connected to the at least one circuit conductor, andsaid transmission line ground plane is in electrical contact with saidconductive plating at the base of said recess.
 7. The assembly of claim1 wherein said component is disposed wholly within said recess.
 8. Theassembly of claim 1 wherein side wall plating integral with said baseplating is disposed at least partially around the walls of said recess.9. The assembly of claim 8 wherein surface plating is located on saidfirst surface of said substrate adjacent said recess, said surfaceplating electrically connected to said recess side wall plating.
 10. Aninterconnection assembly for a component mounted to an electricalcircuit, said circuit comprising at least one conductor mounted on afirst surface of an insulating substrate and ground conductor over asecond surface of the insulating substrate opposite the first surface,the assembly comprising:(a) means forming a recess in the firstsubstrate surface; (b) conductive plating on the first substrate surfacecovering at least a portion of said means forming a recess; (c) said atleast one circuit conductor terminating adjacent to said means forming arecess in the first substrate surface; (d) at least one electricalcomponent carried on a component substrate, said component substratesubtending an area greater than the area subtended by said means forminga recess, said component substrate further including a first surface onwhich said component is mounted, at least one conductor on said firstsurface of said component substrate electrically connected to saidcomponent at at least one end of said conductor, ground platingextending over a second substrate surface opposite said first substratesurface, over edges of said component substrate, and over at least aportion of said first substrate surface, said plating spaced away fromsaid component, said component substrate being mounted to said circuitso that said component is within the space defined by said means forminga recess, said component substrate conductor at least partiallyoverlapping said adjacent circuit conductor, and said componentsubstrate ground plating on said second substrate surface at leastpartially overlapping said circuit substrate first surface adjacent saidrecess and spaced away from said circuit conductor; (e) at least onelow-impedance conductive path between said recess conductive plating tosaid circuit ground conductor extending through said circuit substrate;and (f) at least one low-impedance conductive path between saidcomponent substrate ground plating and said circuit ground conductorextending through said circuit substrate.
 11. The assembly of claim 10wherein said first surface of said circuit substrate underlying saidcomponent substrate ground plating is provided with surface plating, andsaid at least one conductive path extending from said componentsubstrate ground plating to said ground conductor extends from saidcircuit surface plating to said ground conductor.
 12. The assembly ofclaim 10 wherein said conductive paths are each at least one platedthrough hole.
 13. The assembly of claim 10 wherein said conductiveplating in said means forming a recess covers substantially all thesurfaces in said recess.
 14. The assembly of claim 10 wherein saidelectrical circuit is a microstrip circuit and said ground conductor isa conductive ground plane disposed at least partially over said circuitsubstrate second surface.